Method of forming contacts for a back-contact solar cell

ABSTRACT

Methods of forming contacts for back-contact solar cells are described. In one embodiment, a method includes forming a thin dielectric layer on a substrate, forming a polysilicon layer on the thin dielectric layer, forming and patterning a solid-state p-type dopant source on the polysilicon layer, forming an n-type dopant source layer over exposed regions of the polysilicon layer and over a plurality of regions of the solid-state p-type dopant source, and heating the substrate to provide a plurality of n-type doped polysilicon regions among a plurality of p-type doped polysilicon regions.

The invention described herein was made with Governmental support undercontract number DE-FC36-07GO17043 awarded by the United StatesDepartment of Energy. The Government may have certain rights in theinvention.

TECHNICAL FIELD

Embodiments of the present invention are in the field of renewableenergy and, in particular, methods of forming contacts for back-contactsolar cells.

BACKGROUND

Photovoltaic cells, commonly known as solar cells, are well knowndevices for direct conversion of solar radiation into electrical energy.Generally, solar cells are fabricated on a semiconductor wafer orsubstrate using semiconductor processing techniques to form a p-njunction near a surface of the substrate. Solar radiation impinging onthe surface of, and entering into, the substrate creates electron andhole pairs in the bulk of the substrate. The electron and hole pairsmigrate to p-doped and n-doped regions in the substrate, therebygenerating a voltage differential between the doped regions. The dopedregions are connected to conductive regions on the solar cell to directan electrical current from the cell to an external circuit coupledthereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart representing operations in a method offorming contacts for a back-contact solar cell, in accordance with anembodiment of the present invention.

FIG. 2A illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 102 of theflowchart of FIG. 1 and to operation 302 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2B illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 104 of theflowchart of FIG. 1 and to operation 304 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2C illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 106 of theflowchart of FIG. 1 and to operation 306 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2D illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 108 of theflowchart of FIG. 1 and to operation 308 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2E illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operations 308 and 310 ofthe flowchart of FIG. 3, in accordance with an embodiment of the presentinvention.

FIG. 2F illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 110 of theflowchart of FIG. 1 and to operation 314 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2G illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 112 of theflowchart of FIG. 1 and to operation 316 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2H illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 114 of theflowchart of FIG. 1 and to operation 318 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2I illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 116 of theflowchart of FIG. 1 and to operation 320 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2J illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, in accordance with an embodiment of thepresent invention.

FIG. 2K illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, corresponding to operation 118 of theflowchart of FIG. 1 and to operation 322 of the flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 2L illustrates a cross-sectional view of a stage in the fabricationof a back-contact solar cell, in accordance with an embodiment of thepresent invention.

FIG. 3 illustrates a flowchart representing operations in a method offorming contacts for a back-contact solar cell, in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Methods of forming contacts for back-contact solar cells are describedherein. In the following description, numerous specific details are setforth, such as specific process flow operations, in order to provide athorough understanding of embodiments of the present invention. It willbe apparent to one skilled in the art that embodiments of the presentinvention may be practiced without these specific details. In otherinstances, well-known fabrication techniques, such as lithography andpatterning techniques, are not described in detail in order to notunnecessarily obscure embodiments of the present invention. Furthermore,it is to be understood that the various embodiments shown in the figuresare illustrative representations and are not necessarily drawn to scale.

Disclosed herein are methods of forming contacts for back-contact solarcells. In one embodiment, a method includes forming a thin dielectriclayer on a substrate. A polysilicon layer is formed on the thindielectric layer. A solid-state p-type dopant source is formed andpatterned on the polysilicon layer. The patterning exposes regions ofthe polysilicon layer between a plurality of regions of the solid-statep-type dopant source. An n-type dopant source layer is formed over theexposed regions of the polysilicon layer and the plurality of regions ofthe solid-state p-type dopant source. Forming the n-type dopant sourceincludes at least partially driving dopants from the n-type dopantsource layer into the exposed regions of the polysilicon layer to form aplurality of n-type dopant-containing polysilicon regions between theplurality of regions of the solid-state p-type dopant source. Thesubstrate is heated to provide a plurality of n-type doped polysiliconregions among a plurality of p-type doped polysilicon regions.

In another embodiment, a method also includes first forming a thindielectric layer on a substrate. A polysilicon layer is formed on thethin dielectric layer. A solid-state p-type dopant source is formed andpatterned on the polysilicon layer. The patterning exposes regions ofthe polysilicon layer between a plurality of regions of the solid-statep-type dopant source. The substrate is loaded in a reaction chamber and,without removing the substrate from the reaction chamber, an n-typedopant source layer is formed over the exposed regions of thepolysilicon layer and over the plurality of regions of the solid-statep-type dopant source. Further, dopants are at least partially drivenfrom the n-type dopant source layer into the exposed regions of thepolysilicon layer to form a plurality of n-type dopant-containingpolysilicon regions between the plurality of regions of the solid-statep-type dopant source. The substrate is removed from the reactionchamber. Subsequently, the substrate is heated to provide a plurality ofn-type doped polysilicon regions among a plurality of p-type dopedpolysilicon regions.

The formation of contacts for a back-contact solar cell may be performedusing laser ablation to form holes or openings through ananti-reflective coating (ARC) layer formed above an array of p-type andn-type doped regions on the back-side of the solar cell. Conductivecontacts, such as metal contacts, may then be formed in the openings toprovide electrical coupling with the array of p-type and n-type dopedregions. However, in order to facilitate a rapid and reliable laserablation process, it may be desirable to ensure that the totaldielectric thickness over the p-type and n-type doped regions is thinand relatively the same over both the p-type and n-type doped regions.The total dielectric thickness may include the thickness of the ARClayer plus any other dielectric layers formed above the p-type andn-type doped regions, such as solid-state dopant source films likeborosilicate glass (BSG) and, if used, phosphosilicate glass (PSG).

In accordance with an embodiment of the present invention, a dopingoperation for n-type doped regions using a PSG solid-state dopant sourceis replaced with a POCl₃ deposition operation to form, upon mixing withO₂, a layer of P₂O₅. This modification in doping operation may reducethe total number of process operations required to form an array ofp-type and n-type doped regions and may aid in optimizing the drive forensuring that the total dielectric thickness over p-type and the n-typedoped regions is thin and relatively the same over both the p-type andn-type doped regions. Furthermore, in one embodiment, a doping sourcedeposition and at least partial drive is performed in a single chamberof a process tool, with only a single introduction into the processchamber.

FIG. 1 illustrates a flowchart 100 representing operations in a methodsof forming contacts for a back-contact solar cell, in accordance with anembodiment of the present invention. FIGS. 2A-2L illustratecross-sectional views of various stages in the fabrication of aback-contact solar cell, corresponding to operations of flowchart 100,in accordance with an embodiment of the present invention.

Referring to operation 102 of flowchart 100, and to corresponding FIG.2A, a method of forming contacts for a back-contact solar cell includesforming a thin dielectric layer 202 on a substrate 200.

In an embodiment, the thin dielectric layer 202 is composed of silicondioxide and has a thickness approximately in the range of 5-50Angstroms. In one embodiment, the thin dielectric layer 202 performs asa tunneling oxide layer. In an embodiment, substrate 200 is a bulksingle-crystal substrate, such as an n-type doped single crystallinesilicon substrate. However, in an alternative embodiment, substrate 200includes a polycrystalline silicon layer disposed on a global solar cellsubstrate.

Referring to operation 104 of flowchart 100, and to corresponding FIG.2B, the method of forming contacts for the back-contact solar cell alsoincludes forming a polysilicon layer 204 on the thin dielectric layer202. It is to be understood that use of the term polysilicon layer isintended to also cover material that can be described as amorphous- orα-silicon.

Referring to operation 106 of flowchart 100, and to corresponding FIG.2C, the method of forming contacts for the back-contact solar cell alsoincludes forming and patterning a solid-state p-type dopant source 206on the polysilicon layer 204.

In an embodiment, the patterning exposes regions 208 of the polysiliconlayer 204 between a plurality of regions 206 of the solid-state p-typedopant source, as depicted in FIG. 2C. In one embodiment, forming andpatterning the solid-state p-type dopant source 206 includes forming andpatterning a layer of boron silicate glass (BSG). In a specificembodiment, the BSG layer is formed as a uniform, blanket layer and thenpatterned by a lithography and etch process. In another specificembodiment, the BSG layer is deposited already having a pattern and,thus, the forming and patterning are performed simultaneously. In onesuch embodiment, the patterned BSG layer is formed by an ink-jetprinting approach or a screen-printing approach. It is to be understoodthat a solid-state p-type dopant source is a layer of film that includesdopant impurity atoms and can be deposited above a substrate. This is incontrast to an ion implantation approach.

Referring to operation 108 of flowchart 100, and to corresponding FIG.2D, the method of forming contacts for the back-contact solar cell alsoincludes forming an n-type dopant source layer 210 over the exposedregions 208 of the polysilicon layer 204 and over the plurality ofregions 206 of the solid-state p-type dopant source.

In an embodiment, referring to FIG. 2E, the forming includes at leastpartially driving dopants from the n-type dopant source layer 210 intothe exposed regions 208 of the polysilicon layer 204 to form a pluralityof n-type dopant-containing polysilicon regions 212 between theplurality of regions 206 of the solid-state p-type dopant source. In anembodiment, referring again to FIG. 2E, forming the n-type dopant sourcelayer 210 further includes at least partially driving dopants from theplurality of regions 206 of the solid-state p-type dopant source intothe polysilicon layer 204 to form regions 214. In an embodiment, formingthe n-type dopant source layer includes forming a layer of P₂O₅.Subsequently, the n-type dopant source layer 210 may be removed, asdepicted in FIG. 2F.

Referring to operation 110 of flowchart 100, and to corresponding FIG.2F, in one embodiment the method of forming contacts for theback-contact solar cell optionally further includes forming trenches 216between the plurality of n-type dopant-containing polysilicon regions212 and the plurality of regions 206 of the solid-state p-type dopantsource and corresponding regions 214.

In an embodiment, the trenches 216 are formed in the polysilicon layer204, in the thin dielectric layer 202, and partially in the substrate202. In one embodiment, the trenches 216 are formed by using alithography and etch process. In a specific embodiment, different etchoperations are used to pattern polysilicon layer 204 and then substrate200.

Referring to operation 112 of flowchart 100, and to corresponding FIG.2G, in one embodiment the method of forming contacts for theback-contact solar cell optionally further includes, subsequent toforming the trenches 216, texturizing portions 218 of the substrate 200exposed by the trenches 216.

In an embodiment, the texturing provides a random texture pattern. Therandom texturing pattern may be formed by applying an anisotropicetching process to exposed regions of substrate 200 and may thus bedetermined by crystal planes, such single-crystalline silicon planes, ofthe substrate 200. In an embodiment, the forming of the trenches 216 andthe texturizing of substrate 200 are performed without performing a cureoperation between forming the trenches 216 and texturizing the substrate200. Such a cure operation may include a heating operation, exposure toinfra-red (IR) radiation, or exposure to ultra-violet (UV) radiation.

Referring to operation 114 of flowchart 100, and to corresponding FIG.2H, in one embodiment the method of forming contacts for theback-contact solar cell optionally further includes removing theplurality of regions 206 of the solid-state p-type dopant source. In anembodiment, the plurality of regions 206 of the solid-state p-typedopant source are removed by using a wet etch technique by applying awet solution including aqueous hydrofluoric acid or another source ofHF. In an embodiment, the plurality of regions 206 of the solid-statep-type dopant source are removed by plasma etching.

Referring to operation 116 of flowchart 100, and to corresponding FIG.2I, the method of forming contacts for the back-contact solar cell alsoincludes heating 299 the substrate 200 to provide a plurality of n-typedoped polysilicon regions 220 among a plurality of p-type dopedpolysilicon regions 222.

In an embodiment, heating the substrate 200 includes activating thedopants in the plurality of n-type dopant-containing polysilicon regions212 to form the plurality of n-type doped polysilicon regions 220. Inone embodiment, the activating includes changing the incorporation of atleast some of the dopants from interstitial to substitutional withinpolysilicon layer 204. In a specific embodiment, the activating includesproviding the plurality of n-type doped polysilicon regions 220 with alow sheet resistance approximately in the range of 50-300 ohms persquare.

In an embodiment, heating the substrate 200 also includes furthering thedriving of dopants originating from the plurality of regions 206 of thesolid-state p-type dopant source into the polysilicon layer 204, andactivating the dopants in the polysilicon layer 204 to provide theplurality of p-type doped polysilicon regions 222. In one embodiment,the activating includes changing the incorporation of at least some ofthe dopants from interstitial to substitutional within polysilicon layer204. In a specific embodiment, the activating includes providing theplurality of p-type doped polysilicon regions 222 with a low sheetresistance approximately in the range of 50-300 ohms per square.

Referring to FIG. 2J, in an embodiment, the method of forming contactsfor the back-contact solar cell optionally further includes forming adielectric layer 224 above the plurality of n-type doped polysiliconregions 220, the plurality of p-type doped polysilicon regions 222, andthe exposed portions of substrate 200. In one embodiment, a lowersurface of the dielectric layer 224 is formed conformal with theplurality of n-type doped polysilicon regions 220, the plurality ofp-type doped polysilicon regions 222, and the exposed portions ofsubstrate 200, while an upper surface of dielectric layer 224 issubstantially flat, as depicted in FIG. 2J. In a specific embodiment,the dielectric layer 224 is an anti-reflective coating (ARC) layer.

Referring to operation 118 of flowchart 100, and to corresponding FIG.2K, in an embodiment the method of forming contacts for the back-contactsolar cell optionally further includes forming, by laser abalation, aplurality of contact openings 226 to the plurality of n-type dopedpolysilicon regions 220 and to the plurality of p-type doped polysiliconregions 222. In one embodiment, the contact openings 226 to the n-typedoped polysilicon regions 220 have substantially the same height as thecontact openings to the p-type doped polysilicon regions 222, asdepicted in FIG. 2K.

Referring to FIG. 2L, in an embodiment, the method of forming contactsfor the back-contact solar cell optionally further includes formingconductive contacts 228 in the plurality of contact openings 226 andcoupled to the plurality of n-type doped polysilicon regions 220 and tothe plurality of p-type doped polysilicon regions 222. In an embodiment,the conductive contacts 228 are composed of metal and are formed by adeposition, lithographic, and etch approach.

In another aspect of the present invention, an n-type dopant source isformed above a polysilicon layer and a p-type dopant source, and thenn-type and p-type dopants are driven into the polysilicon layer, withoutever removing a corresponding underlying substrate from a reactionchamber. For example, FIG. 3 illustrates a flowchart 300 representingoperations in a methods of forming contacts for a back-contact solarcell, in accordance with an embodiment of the present invention. FIGS.2A-2L illustrate cross-sectional views of various stages in thefabrication of a back-contact solar cell, corresponding to operations offlowchart 300, in accordance with an embodiment of the presentinvention.

Referring to operation 302 of flowchart 300, and to corresponding FIG.2A, a method of forming contacts for a back-contact solar cell includesforming a thin dielectric layer 202 on a substrate 200.

In an embodiment, the thin dielectric layer 202 is composed of silicondioxide and has a thickness approximately in the range of 5-50Angstroms. In one embodiment, the thin dielectric layer 202 performs asa tunneling oxide layer. In an embodiment, substrate 200 is a bulksingle-crystal substrate, such as an n-type doped single crystallinesilicon substrate. However, in an alternative embodiment, substrate 200includes a polycrystalline silicon layer disposed on a global solar cellsubstrate.

Referring to operation 304 of flowchart 300, and to corresponding FIG.2B, the method of forming contacts for the back-contact solar cell alsoincludes forming a polysilicon layer 204 on the thin dielectric layer202. It is to be understood that use of the term polysilicon layer isintended to also cover material that can be described as amorphous- orα-silicon.

In an embodiment, the patterning exposes regions 208 of the polysiliconlayer 204 between a plurality of regions 206 of the solid-state p-typedopant source, as depicted in FIG. 2C. In one embodiment, forming andpatterning the solid-state p-type dopant source 206 includes forming andpatterning a layer of boron silicate glass (BSG). In a specificembodiment, the BSG layer is formed as a uniform, blanket layer and thenpatterned by a lithography and etch process. In another specificembodiment, the BSG layer is deposited already having a pattern and,thus, the forming and patterning are performed simultaneously. In onesuch embodiment, the patterned BSG layer is formed by an ink-jetprinting approach or a screen-printing approach. It is to be understoodthat a solid-state p-type dopant source is a layer of film that includesdopant impurity atoms and can be deposited above a substrate. This is incontrast to an ion implantation approach.

Referring to operation 308 of flowchart 300, and to corresponding FIGS.2D and 2E, the method of forming contacts for the back-contact solarcell also includes loading the substrate 200 in a reaction chamber.Without removing the substrate 200 from the reaction chamber, an n-typedopant source layer 210 is formed over the exposed regions 208 of thepolysilicon layer 204 and over the plurality of regions 206 of thesolid-state p-type dopant source. Dopants from the n-type dopant sourcelayer 210 are at least partially driving into the exposed regions 208 ofthe polysilicon layer 204 to form a plurality of n-typedopant-containing polysilicon regions 212 between the plurality ofregions 206 of the solid-state p-type dopant source.

In an embodiment, referring again to FIG. 2E, forming the n-type dopantsource layer 210 further includes at least partially driving dopantsfrom the plurality of regions 206 of the solid-state p-type dopantsource into the polysilicon layer 204 to form regions 214. In anembodiment, forming the n-type dopant source layer includes forming alayer of P₂O₅. It is noted that it may be the case that driving (ordriving to a further extent) dopants from the plurality of regions 206of the solid-state p-type dopant source into the polysilicon layer 204to form regions 214 requires an additional operation in the processchamber in addition to only the formation of n-type dopant source layer210. For example, in an embodiment referring to optional operation 310of flowchart 300, the method further includes a separate operationwherein, while the substrate 200 is still loaded in the reactionchamber, dopants from the solid-state p-type dopant source are at leastpartially driven into the polysilicon layer 204 to form, or to furtherformation of, regions 214. In an embodiment, operation 310 involvesheating the substrate 200 well above the temperature of the operationdescribed in association with operation 308.

Referring to operation 312 of flowchart 300, the method of formingcontacts for the back-contact solar cell also includes, subsequent tothe above process operations have been performed in a singleintroduction of substrate 200 into the reaction chamber, removing thesubstrate 200 from the reaction chamber. Subsequently, the n-type dopantsource layer 210 may be removed, as depicted in FIG. 2F.

Referring to operation 314 of flowchart 300, and to corresponding FIG.2F, in one embodiment the method of forming contacts for theback-contact solar cell optionally further includes forming trenches 216between the plurality of n-type dopant-containing polysilicon regions212 and the plurality of regions 206 of the solid-state p-type dopantsource and corresponding regions 214.

In an embodiment, the trenches 216 are formed in the polysilicon layer204, in the thin dielectric layer 202, and partially in the substrate202. In one embodiment, the trenches 216 are formed by using alithography and etch process. In a specific embodiment, different etchoperations are used to pattern polysilicon layer 204 and then substrate200.

Referring to operation 316 of flowchart 300, and to corresponding FIG.2G, in one embodiment the method of forming contacts for theback-contact solar cell optionally further includes, subsequent toforming the trenches 216, texturizing portions 218 of the substrate 200exposed by the trenches 216.

In an embodiment, the texturing provides a random texture pattern. Therandom texturing pattern may be formed by applying an anisotropicetching process to exposed regions of substrate 200 and may thus bedetermined by crystal planes, such single-crystalline silicon planes, ofthe substrate 200. In an embodiment, the forming of the trenches 216 andthe texturizing of substrate 200 are performed without performing a cureoperation between forming the trenches 216 and texturizing the substrate200. Such a cure operation may include a heating operation, exposure toinfra-red (IR) radiation, or exposure to ultra-violet (UV) radiation.

Referring to operation 318 of flowchart 300, and to corresponding FIG.2H, in one embodiment the method of forming contacts for theback-contact solar cell optionally further includes removing theplurality of regions 206 of the solid-state p-type dopant source. In anembodiment, the plurality of regions 206 of the solid-state p-typedopant source are removed by using a wet etch technique by applying awet solution including aqueous hydrofluoric acid or another source ofHF. In an embodiment, the plurality of regions 206 of the solid-statep-type dopant source are removed by plasma etching.

Referring to operation 320 of flowchart 300, and to corresponding FIG.2I, the method of forming contacts for the back-contact solar cell alsoincludes heating 299 the substrate 200 to provide a plurality of n-typedoped polysilicon regions 220 among a plurality of p-type dopedpolysilicon regions 222.

In an embodiment, heating the substrate 200 includes activating thedopants in the plurality of n-type dopant-containing polysilicon regions212 to form the plurality of n-type doped polysilicon regions 220. Inone embodiment, the activating includes changing the incorporation of atleast some of the dopants from interstitial to substitutional withinpolysilicon layer 204. In a specific embodiment, the activating includesproviding the plurality of n-type doped polysilicon regions 220 with alow sheet resistance approximately in the range of 50-300 ohms persquare.

In an embodiment, heating the substrate 200 also includes furthering thedriving of dopants originating from the plurality of regions 206 of thesolid-state p-type dopant source into the polysilicon layer 204, andactivating the dopants in the polysilicon layer 204 to provide theplurality of p-type doped polysilicon regions 222. In one embodiment,the activating includes changing the incorporation of at least some ofthe dopants from interstitial to substitutional within polysilicon layer204. In a specific embodiment, the activating includes providing theplurality of p-type doped polysilicon regions 222 with a low sheetresistance approximately in the range of 50-300 ohms per square.

Referring to FIG. 2J, in an embodiment, the method of forming contactsfor the back-contact solar cell optionally further includes forming adielectric layer 224 above the plurality of n-type doped polysiliconregions 220, the plurality of p-type doped polysilicon regions 222, andthe exposed portions of substrate 200. In one embodiment, a lowersurface of the dielectric layer 224 is formed conformal with theplurality of n-type doped polysilicon regions 220, the plurality ofp-type doped polysilicon regions 222, and the exposed portions ofsubstrate 200, while an upper surface of dielectric layer 224 issubstantially flat, as depicted in FIG. 2J. In a specific embodiment,the dielectric layer 224 is an anti-reflective coating (ARC) layer.

Referring to operation 322 of flowchart 300, and to corresponding FIG.2K, in an embodiment the method of forming contacts for the back-contactsolar cell optionally further includes forming, by laser ablation, aplurality of contact openings 226 to the plurality of n-type dopedpolysilicon regions 220 and to the plurality of p-type doped polysiliconregions 222. In one embodiment, the contact openings 226 to the n-typedoped polysilicon regions 220 have substantially the same height as thecontact openings to the p-type doped polysilicon regions 222, asdepicted in FIG. 2K.

Referring to FIG. 2L, in an embodiment, the method of forming contactsfor the back-contact solar cell optionally further includes formingconductive contacts 228 in the plurality of contact openings 226 andcoupled to the plurality of n-type doped polysilicon regions 220 and tothe plurality of p-type doped polysilicon regions 222. In an embodiment,the conductive contacts 228 are composed of metal and are formed by adeposition, lithographic, and etch approach.

Thus, methods of forming contacts for back-contact solar cells have beendisclosed. In accordance with an embodiment of the present invention, amethod includes forming a thin dielectric layer on a substrate. Themethod also includes forming a polysilicon layer on the thin dielectriclayer. The method also includes forming and patterning a solid-statep-type dopant source on the polysilicon layer, the patterning exposingregions of the polysilicon layer between a plurality of regions of thesolid-state p-type dopant source. The method also includes forming ann-type dopant source layer over the exposed regions of the polysiliconlayer and the plurality of regions of the solid-state p-type dopantsource, the forming comprising at least partially driving dopants fromthe n-type dopant source layer into the exposed regions of thepolysilicon layer to form a plurality of n-type dopant-containingpolysilicon regions between the plurality of regions of the solid-statep-type dopant source. The method also includes heating the substrate toprovide a plurality of n-type doped polysilicon regions among aplurality of p-type doped polysilicon regions. In one embodiment, themethod also includes, subsequent to forming an n-type dopant sourcelayer and prior to heating the substrate, forming trenches between theplurality of n-type dopant-containing polysilicon regions and theplurality of regions of the solid-state p-type dopant source, thetrenches formed in the polysilicon layer, in the thin dielectric layer,and partially in the substrate.

What is claimed is:
 1. A method of forming contacts for a back-contactsolar cell, the method comprising: forming a thin dielectric layer on asubstrate; forming a polysilicon layer on the thin dielectric layer;forming and patterning a solid-state p-type dopant source on thepolysilicon layer, the patterning exposing regions of the polysiliconlayer between a plurality of regions of the solid-state p-type dopantsource; forming an n-type dopant source layer over the exposed regionsof the polysilicon layer and the plurality of regions of the solid-statep-type dopant source, the forming comprising at least partially drivingdopants from the n-type dopant source layer into the exposed regions ofthe polysilicon layer to form a plurality of n-type dopant-containingpolysilicon regions between the plurality of regions of the solid-statep-type dopant source; and, subsequently, heating the substrate toprovide a plurality of n-type doped polysilicon regions among aplurality of p-type doped polysilicon regions and, prior to the heating,removing the plurality of regions of the solid-state p-type dopantsource.
 2. The method of claim 1, further comprising: subsequent toforming an n-type dopant source layer and prior to heating thesubstrate, forming trenches between the plurality of n-typedopant-containing polysilicon regions and the plurality of regions ofthe solid-state p-type dopant source, the trenches formed in thepolysilicon layer, in the thin dielectric layer, and partially in thesubstrate.
 3. The method of claim 2, further comprising: subsequent toforming the trenches and prior to heating the substrate, texturizingportions of the substrate exposed by the trenches.
 4. The method ofclaim 3, wherein forming the trenches and the texturizing is performedwithout a cure operation between the forming the trenches and thetexturizing.
 5. The method of claim 1, wherein forming the n-type dopantsource layer further comprises at least partially driving dopants fromthe plurality of regions of the solid-state p-type dopant source intothe polysilicon layer.
 6. The method of claim 5, wherein heating thesubstrate comprises activating the dopants in the plurality of n-typedopant-containing polysilicon regions, furthering the driving of dopantsoriginating from the plurality of regions of the solid-state p-typedopant source into the polysilicon layer, and activating the dopants ofthe plurality of regions of the solid-state p-type dopant source in thepolysilicon layer.
 7. The method of claim 1, wherein forming andpatterning the solid-state p-type dopant source comprises forming andpatterning a layer of boron silicate glass (BSG).
 8. The method of claim1, wherein forming the n-type dopant source layer comprises forming alayer of P₂O₅.
 9. The method of claim 1, further comprising: forming, bylaser ablation, a plurality of contact openings to the plurality ofn-type doped polysilicon regions and the plurality of p-type dopedpolysilicon regions.
 10. A solar cell fabricated according to the methodof claim
 1. 11. A method of forming contacts for a back-contact solarcell, the method comprising: forming a thin dielectric layer on asubstrate; forming a polysilicon layer on the thin dielectric layer;forming and patterning a solid-state p-type dopant source on thepolysilicon layer, the patterning exposing regions of the polysiliconlayer between a plurality of regions of the solid-state p-type dopantsource; loading the substrate in a reaction chamber and, withoutremoving the substrate from the reaction chamber, both forming an n-typedopant source layer over the exposed regions of the polysilicon layerand the plurality of regions of the solid-state p-type dopant source andat least partially driving dopants from the n-type dopant source layerinto the exposed regions of the polysilicon layer to form a plurality ofn-type dopant-containing polysilicon regions between the plurality ofregions of the solid-state p-type dopant source; removing the substratefrom the reaction chamber; and, subsequently, heating the substrate toprovide a plurality of n-type doped polysilicon regions among aplurality of p-type doped polysilicon regions.
 12. The method of claim11, further comprising: subsequent to forming an n-type dopant sourcelayer and prior to heating the substrate, forming trenches between theplurality of n-type dopant-containing polysilicon regions and theplurality of regions of the solid-state p-type dopant source, thetrenches formed in the polysilicon layer, in the thin dielectric layer,and partially in the substrate.
 13. The method of claim 12, furthercomprising: subsequent to forming the trenches and prior to heating thesubstrate, texturizing portions of the substrate exposed by thetrenches.
 14. The method of claim 13, wherein forming the trenches andthe texturizing is performed without a cure operation between theforming the trenches and the texturizing.
 15. The method of claim 11,wherein forming the n-type dopant source layer further comprises atleast partially driving dopants from the plurality of regions of thesolid-state p-type dopant source into the polysilicon layer.
 16. Themethod of claim 15, wherein heating the substrate comprises activatingthe dopants in the plurality of n-type dopant-containing polysiliconregions, furthering the driving of dopants originating from theplurality of regions of the solid-state p-type dopant source into thepolysilicon layer, and activating the dopants of the plurality ofregions of the solid-state p-type dopant source in the polysiliconlayer.
 17. The method of claim 11, further comprising: while thesubstrate is loaded in the reaction chamber, at least partially drivingdopants from the solid-state p-type dopant source into the polysiliconlayer.
 18. A solar cell fabricated according to the method of claim 11.